1. Field
The present invention relates in general to bias generator circuits, and more specifically to bias generators with minimized susceptibility to environmental and manufacturing changes.
2. Background
A bias generator provides a bias voltage to a device such as transistor to allow the device to operate in a preferred region of the device operational characteristics. In many applications, the selection of the relative sizes of the transistors used in the bias generator and the load device is critical to maintain the operational characteristics within an acceptable region over variances due to temperature and manufacturing. For example, bias generators are often used to set a voltage at an input of a low noise amplifier (LNA) transistor where small changes in operational characteristics result in increased noise and non-linear input to output relationships. Since the devices used to implement bias generators are susceptible to temperature and manufacturing process variations, conventional biasing schemes attempt to minimize the effects of temperature and process fluctuations. In an attempt to maximize the performance of the biased device, conventional bias generates consume significant amounts of current relative to the current used by the biased device. Performance of bias generators typically suffers when the devices in the bias generator are mismatched from the biased device. A mismatch between devices causes time-independent random variations in physical characteristics of identically designed devices. Typical characteristics that may be different between mismatched devices include device dimensions, threshold voltage, and mobility. Performance of a bias generator is typically improved by selecting a biasing device similar to the biased device. Unfortunately, conventional biasing schemes typically require a significant tradeoff between current draw and relative device size between the biased device and the devices in the bias generator.
Therefore, there is a need for a bias generator with minimized current consumption and maximized performance.